1. Field of the Invention
The present invention generally relates to an electromagnetic powder coupling device, and more particularly to a cooling system applicable to an electromagnetic powder coupling devices including a clutch and or a brake.
2. Prior Art
Major components of the general type industrial electromagnetic powder coupling device consisting of, a field assembly incorporating therein a magnetic coil, a driving clutch referred to a cylinder, a rotor as a driven clutch member and magnetic powder, merely referred to "powder" being filled in a gap defined between the cylinder as a driving clutch and a driven clutch, which gap is usually referred to as an actuating gap.
The following describes the general function of an electromagnetic powder coupling device with reference to FIG. 1.
When a cylinder 5 is rotated being driven by an external driving shaft or by an attached driving shaft 4 with the coil 8 of a field member 9 without being excited, the powder in the gap is urged by centrifugal force against the inner wall of the cylinder 5, and thus an annular space is formed between the coalesced surface of the magnetic powder and a rotor 10. As a result no appreciable amount of torque can be formed under this state of non-contact between the powder and the rotor 10 which are spaced apart.
On the other hand, when the field coil 8 is excited, a closed path of magnetic flux .phi. is established as shown by a dash line in FIG. 1. EQU Field member.fwdarw.Cylinder.fwdarw.Rotor.fwdarw.Cylinder.fwdarw.Field member.
Then the magnetic powder aligns in the gap along the path of the magnetic flux .phi. in the assembly and couples the cylinder 5 with the rotor 10, thereby the driving force can be transmitted from the cylinder 5 to the rotor by virtue of the shear resistance of the magnetic powder.
Since FIG. 1 is shown as an electromagnetic powder brake the rotor 10 is fixed stationary by a fixed rotor boss 10c, however, if this coupling device is to be used as a clutch, the rotor 10 is connected to an output shaft(not shown)which can be rotatable integral with the rotor 10.
Because of the fact that it utilizes magnetic powder as a power transmitting medium and thus the coupling devices of this kind have such feature as capable of imparting constant torque even under slipping conditions which other coupling means cannot satisfy, it can be operated with stable control under continued slipping(slippage), however, it has been deemed that the most important problems to be solved is how to cool and remove the heat generated by the aforesaid continued slipping which is not encountered in any other friction disc type coupling means.
In view of the above-mentioned problem, there have been proposed a number of cooling systems up to the present, such as water coolled, natural cooling and forced draft air cooling using an air blower or blowers, among which the water cooling has been found to be most satisfatory so far as its cooling efficiency is concerned, however, it has found to have several drawbacks such as troublesome work in piping, leakage of water in use and the related parts of the device are liable to be dewed.
As a measure to solve the drawbacks encountered in the water cooling system of the prior art as mentioned above, the natural cooling means as shown in FIG. 1 has been proposed as a typical one, which radiates(dissipates) both frictional heat and Joule heat generated by a rotor 10 and a cylinder 5 through the surfaces of a bracket 2 and a bracket 3 contacting the outer atmosphere, and also dissipates the Joule heat generated by the field 9 through the surface of the field 9.
Shown in FIG. 2 is a forced air draft type cooling means adopted in an electromagnetic powder brake capable of cooling its field member 9 and brackets 22 for holding the field member 9 and having no such appreciable drawbacks as found in the water cooling system as mentioned above.
As shown in FIG. 2, the cooling means comprises, a blower 1 attached to the bracket 22 disposed at the output side of the coupling device, and cooling fins 5a supported by a side plate 26 and are rotatable integral with the input shaft 4 and positioned axially outside the cylinder 5 and at the portion between the blower 1 and the cylinder 5.
As would be readily recongnized by one skilled in the art, in FIG. 2, numeral 20c denotes a fixed rotor boss for stationarily fixing the rotor 20. The rotor boss 20c carries a labrinth ring 20d, which coacts with another labyrinth ring 26a slantedly stemming out from the side plate 26. The labyrinth rings 20d and 26a are thus disposed to act as a pair to prevent magnetic powders in and near the upper part of the gap between the cylinder 5 and the rotor 20 from leaking outward when the field member 9 is not energized. Rather, the labyrinth ring arrangement guides the powders to enter into the opposite lower part of the gap, by guiding the powders to flow downward through two circumferential paths defined by the pair of labyrinth rings 20d and 26a.
The cooling means further comprises a heat pipe 20a of highly heat conductive material and including a cooling fin 20b which is secured to and being in tight contact with the rotor 20 at its axially central portion and axially extends toward the outlet of aforesaid blower 1.
Numeral 4 disposed at the input side is an input shaft 4 which usually is an external driving shaft to be connected at the user's site.
The cylinder 5 is fixed to the input shaft 4 through a side plate 7 and being spaced apart at a gap of specified extent from the outer periphery of the rotor 20.
As can be seen from FIG. 1, such cooling system which dissipates heat generated by means of heat conduction through the contact with air at the surface or surfaces of the brackets at both axial ends and the surface of the field member, is no more than a natural cooling. As a result, the cooling effect of such a cooling system cannot be expected to be high enough and the efficiency in slippage also becomes low, which giving rise to a low allowable capacity limit as compared with those of a water cooled system.
As to the forced draft cooling system shown in FIG. 2, constituting members effective for cooling are the heat pipe 20a and fin 20b for cooling the rotor 20 and the bracket 22, and the fin 5a for cooling the cylinder 5, therefore, the cooling air from the blower 1 flows, as a uniflow type of stream K, passing through the fin 20b then flows somewhat slantedly in radial direction outwards, as a consequence, the heat generated at the actuating part of the coupling device is transmitted to the field member 9 through the bracket 22. In addition. Joule heat generated at the coil is also added to the field member 9, then the cooling power also becomes insufficient and thus results in lower slip efficiency as compared with that obtainable by the water cooled system.